1. Field of the Invention
The present invention relates to measuring differential pressure in a conduit, and more particularly relates to measuring differential pressure across a soot filter in the presence of a change in conduit diameter.
2. Description of the Related Art
Recent emissions regulations have required the use of aftertreatment components in many internal combustion engine applications. Many aftertreatment components utilize a differential pressure measurement to control various aspects of the component. For example, particulate filters capture soot from the exhaust stream, and the captured soot is later oxidized and vented to the atmosphere as carbon dioxide or carbon monoxide. The differential pressure across the particulate filter may be used to determine how much soot remains on the particulate filter. If excessive soot is allowed to build up on the particulate filter, the rate of soot oxidation can generate large amounts of heat in a short period of time and cause temperature spikes and large temperature gradients. Temperature spikes can melt the particulate filter, while temperature gradients can cause cracking or other stress related failures.
Many control mechanisms for particulate filters rely partially or completely on a differential pressure measurement to predict the amount of particulate loading on the filter. If the measurement is consistently higher than the true differential pressure, regeneration events of the particulate filter may be too frequent, resulting in loss of fuel economy and filter fatigue failure before the design life is complete. If the measurement is consistently lower than the true differential pressure, the actual particulate loading in the filter may be higher than the intended design, resulting in an increased risk of runaway oxidation of particulates and an uncontrolled regeneration event, often resulting in the complete failure of the particulate filter.
The physical layout of many applications requires that the exhaust systems change diameter along the length of the fluid conduit. When the exhaust system changes diameter near the particulate filter, the differential pressure measurement in a conventional system is not as reliable. For example, when the diameter increases downstream of the particulate filter, the differential pressure appears to be greater than the actual value in most systems. If the diameter decreases downstream of the particulate filter, the differential pressure appears to be lower than the actual value in most systems.
In the current technology, these variations are accounted for in the controls software of the application. The computer calculates the effect of the flow area change on the differential pressure according to the flow rate, temperature, particulate loading, and other variables. Such calculation results in an intensive modeling and calibration effort for each application, and a modest change in the system requires a different calibration. Further, these models are only modestly able to correct for all of the variables, and still suffer from significant offsets between the true and modeled differential pressure.
From the foregoing discussion, applicant asserts that a need exists for an apparatus, system, and method that provides for differential pressure measurement across a conduit flow area change in an aftertreatment system. Beneficially, such an apparatus, system, and method would achieve accurate differential pressure measurements in a simple, reliable fashion that reduces the calibration and modeling efforts required for each application.